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vertebrates

Abstract:

Prairie dogs (Cynomys spp.) are burrowing rodents considered to be ecosystem engineers and keystone species of the central grasslands of North America. Yet, prairie dog populations have declined by an estimated 98% throughout their historic range. This dramatic decline has resulted in the widespread loss of their important ecological role throughout this grassland system. The 92,060 ha Sevilleta NWR in central New Mexico includes more than 54,000 ha of native grassland. Gunnison’s prairie dogs (C. gunnisoni) were reported to occupy ~15,000 ha of what is now the SNWR during the 1960’s, prior to their systematic eradication. In 2010, we collaborated with local agencies and conservation organizations to restore the functional role of prairie dogs to the grassland system. Gunnison’s prairie dogs were reintroduced to a site that was occupied by prairie dogs 40 years ago. This work is part of a larger, long-term study where we are studying the ecological effects of prairie dogs as they re-colonize the grassland ecosystem.

Data set ID:

236

Additional Project roles:

401

Core Areas:

Keywords:

Related sites:

Prairie Dog Town

Methods:

Experimental Design

Four replicate paired 16 ha plots were established in spring 2010. Each pair consists of a treatment plot with prairie dogs (reintroduced), which are plots B and D and a control plot with no prairie dogs (plots A and C). The closest distance between adjacent plots, either within a block or between blocks, is 200 m (Figure 1). The treatment and control within each pair were randomly assigned. Each plot is a 400x400 m on 9x9 grid array with systematically located sample locations for 81 vegetation quadrats. There are also 4 more plots, E and H are control plots and F and G are treatment plots. F and G have been equipped with artificial burrows and are release sites. However, E and H were not set up to do vegetation quads.

Trapping Period

Prairie dogs will be sampled using capture-recapture methods in the summer (3rd week of June) each year and spring (last week of March) and fall when possible.

Pre-baiting Procedure

Set 150 traps within each 300m x 300m trapping area. Place traps in pairs near active burrows at least 4 days prior to trapping. At this time trap doors should be wired open (make certain all traps are properly wired open) with bait trailing from the outside into the back of (or through) the trap. Traps should be baited with sweet feed. Make sure that all traps are functioning properly by testing the trap door sensitivity and adjusting with pliers if needed. Pre-bait traps every morning for 3 days total. All pairs of traps should be numbered with one pin flag for each pair (1-75). All trap pairs should also be GPSed by their number and have maps made for ease of locating traps during trapping.

Trapping Procedures

On the morning of the first trapping day, well before sunrise, the wire should be removed from the traps and the traps then set and baited to capture animals. This can also be done the day before trapping begins. Prairie dogs should be trapped for 3 consecutive mornings.Each morning of trapping, make sure that the traps are all opened well before sunrise, so animals are not disturbed by human activity. This is very important. Traps should only be left opened during the early morning period, until about 10:00 or 11:00 am, depending on the weather conditions and time of year. Prairie dog activity declines by 10:00-11:00, so even if the weather conditions are fine for continued trapping, trap success after this time will decline. Traps should be collected by around 9:00 am, depending on the weather conditions and time of year, and all trapped animals should be brought to a common processing station. The team walks the plot to make sure and check every trap for dogs. As dogs are found trapped, a piece of masking tape is attached to the front of the trap, labeled with the trap number so that that animal can be released where it was trapped. Animals at the processing site should be kept at all times in the shade and carrots should be given to provide moisture during the heat and stress. Once animals have been processed they should be released into their burrow, at the location of their capture. All traps should then be closed for the day. To make sure all are closed, one person should close all the traps from one of the plots and mark the number on the GPS sheet to note the trap has been closed. This can also be done as a team effort, but traps need to be checked twice to make sure they are all closed.

Abstract:

Environmental temperature influences virtually all aspects of organismal performance, including fitness. And since temperature varies throughout space and time, organisms must regularly compete for optimal thermal habitats, much as they do for other resources (e.g. territory, food, or females). However, competition for thermal resources imposes costs, often in the form of a stress response (i.e. increased corticosterone production). Elevated corticosterone promotes physiological and behavioral responses that can increase an organism’s chance of survival, but if left in an organism’s system for too long, it will reduce immunity, degenerate neurons, and lower fitness. Previous theoretical and empirical work indicates that, all else being equal, patchy thermal landscapes reduce the energetic cost of thermoregulation. Therefore, I hypothesize that lizards exposed to patchy distributions of preferred temperatures will have less stress (and thus lower levels of corticosterone) than those exposed to clumped distributions. Furthermore, patchily distributed resources are more difficult for territorial males to monopolize, and thus, subordinate males in patchy thermal landscapes should experience less stress than subordinate males in clumped thermal landscapes.

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Keywords:

Related sites:

Field Station Mixed Shrub

Methods:

Experimental design: Starting in the July of 2012, I will initiate this project as part of a continuing large-scale field study at Sevilleta LTER site in collaboration with PI Michael Angilletta’s Spatially Explicit Theory of Thermoregulation project. As in past research conducted in 2008, 2009 and 2011, I will use male Yarrow’s spiny lizard. This lizard thermoregulates accurately in the absence of predators14,15 and aggressively defends resources from conspecific males14,16.

Nine outdoor arenas (20 x 20 m), consisting of sheet metal walls and a canopy of shade cloth, will be used to manipulate the thermal environments. Among the arenas, three patterns of shade patches will be replicated three times each to generate distinct thermal landscapes (see Figure 1). Lizards will be paired by size: large dominant (22-30 g) with a small subordinate (15-21 g). Each pair (n = 12) will be randomly assigned one of the thermal environments. Prior to each trial, males will be habituated to their arenas for 10 days. During this period, each male will be exposed to the thermal arena every other day (for a 24-h period) in the absence of a competitor (total of 5 days per animal). After the habituation period, males will be placed in arenas for a 4-day testing period. Males will spend two of these days in isolation and the other two in competition. Half the pairs will start the trial in isolation (solitary treatment), and the other half of the pairs will start the trial in competition (social treatment). A matched pair of lizards will be placed together in one arena, and the other two arenas will each have one individual (either small or large) placed into it. After two days, all lizards will be captured and blood samples will be collected within three minutes (speed of collection is necessary to prevent handling stress from affecting plasma corticosterone levels17). Blood will be taken from the orbital sinus with a glass capillary tube and then taken back to the lab where the plasma will be obtained through centrifugation. Plasma will be stored at -80˚C for hormone assays18. After bleeding, solitary lizards will be placed together in one arena, and the previously paired individuals will be separated and split between the two remaining arenas. Thus, a completed habituation and observation set for six pairs (two pairs per type of thermal environment) will take 14 days. And 3 sets will be conducted per season giving a total of 18 pairs per season in each thermal environment (54 pairs in isolation and competition per season). Mixed modeling procedures in the statistical software R will be used to quantify the effects of competition and thermal patchiness on the corticosterone levels of lizards19.

Abstract:

In many ecosystems, seasonal shifts in temperature and precipitation induce pulses of primary productivity that vary in phenology, abundance and nutritional quality. Variation in these resource pulses could strongly influence community composition and ecosystem function, because these pervasive bottom-up forces play a primary role in determining the biomass, life cycles and interactions of organisms across trophic levels. The focus of this research is to understand how consumers across trophic levels alter resource use and assimilation over seasonal and inter-annual timescales in response to climatically driven changes in pulses of primary productivity. We measured the carbon isotope ratios (d13C) of plant, arthropod, and lizard tissues in the northern Chihuahuan Desert to quantify the relative importance of primary production from plants using C3 and C4 photosynthesis for consumers. Summer monsoonal rains on the Sevilleta LTER in New Mexico support a pulse of C4 plant production that have tissue d13C values distinct from C3 plants. During a year when precipitation patterns were relatively normal, d13C measurements showed that consumers used and assimilated significantly more C4 derived carbon over the course of a summer; tracking the seasonal increase in abundance of C4 plants. In the following spring, after a failure in winter precipitation and the associated failure of spring C3 plant growth, consumers showed elevated assimilation of C4 derived carbon relative to a normal rainfall regime. These findings provide insight into how climate, pulsed resources and temporal trophic dynamics may interact to shape semi-arid grasslands such as the Chihuahuan Desert in the present and future.

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Keywords:

Related sites:

Five Points Creosote (C)

Methods:

Study site:

This research was conducted on the Sevilleta LTER, located 100 km south of Albuquerque, New Mexico, which is an ecotonal landscape of Chihuahuan desert shrub and grasslands (Muldavin et al. 2008). Data were collected from a 0.9 x 0.5km strip of land that encompassed a flat bajada and a shallow rocky canyon of mixed desert shrub and grassland dominated by the creosote bush (Larrea tridentata) and black grama grass (Bouteloua eriopoda).

Tissue collection & sample preparation for stable isotope analysis:

From May to October of 2005 and 2006 we collected plant, lizard, and arthropod tissues for carbon stable isotope analysis. During mid-summer of 2005, we randomly collected leaf and stem samples from the 38 most abundant species of plants; these species produce over 90% of the annual biomass on our study site (see Appendix Table A). Approximately 3.5 mg of plant material was then loaded into pre-cleaned tin capsules for isotope analysis.

All animal research was conducted with the approval of the institutional animal care and use committee (UNM-IACUC #05MCC004). Lizards were captured by hand using noose poles and by drift fence and pitfall trap arrays (Enge 2001) randomly scattered over a 0.5 km2 area. Each lizard was toe clipped for permanent identification and snout-vent length (SVL), body mass (g) and sex were recorded. For stable isotope analysis, we obtained a 50 μL blood sample from each lizard and only sampled individuals once in a two week period. We acquired a total of 367 blood samples from 11 lizard species. Blood samples were obtained by slipping a micro-capillary tube (Fisherbrand heparinized 50μL capillary tubes) ventral and posterior to the eyeball to puncture the retro-orbital sinus. Before and after this procedure a local anesthesia (0.5% tetracaine hydrochloride ophthalmic solution, Akorn Inc.) was applied to the eye. Blood samples were stored on ice and centrifuged within 24 hours to separate plasma and red blood cells. For isotope analysis 15 μL of plasma were pipetted into a tin capsule, air dried, and then folded.

Arthropods were captured bi-weekly from May through October of each year in pitfall traps (see above), as well as by hand and sweep netting. Individuals were frozen, lyophilized, ground into a fine powder and 0.5 mg samples were loaded into tin capsules for isotope analysis.

Stable isotope analysis:

Carbon isotope ratios of samples were measured on a continuous flow isotope ratio mass spectrometer (Thermo-Finnigan IRMS Delta Plus) with samples combusted in a Costech ECS 4010 Elemental Analyzer in the UNM Earth and Planetary Sciences Mass Spectrometry lab. The precision of these analyses was ± 0.1‰ SD for δ13C. A laboratory standard calibrated against international standards (valine δ13C -26.3‰ VPDB [Vienna Pee Dee Belemnite Standard]) was included on each run in order to make corrections to raw values. Stable isotope ratios are expressed using standard delta notation (δ) in parts per thousand (‰) as: δX = (Rsample /Rstandard – 1) x 1000, where Rsample and Rstandard are the molar ratios of 13C/12C of a sample and standard.

Estimation of C3 and C4 carbon incorporation into arthropods and lizards:

We used d13C values of consumer tissues and a two-end-point mixing model to estimate the proportion of a consumer’s assimilated carbon that was derived from each plant photosynthetic type (Martinez del Rio and Wolf 2005):

In this model p is the fraction of dietary C4 plant material incorporated into a sampled tissue. We chose to analyze the isotope composition of whole bodies for arthropods because this best reflects the diet of lizards. For lizards we chose plasma because it has a rapid 13C turnover rate with an inter-specific retention time ranging from 25 to 44 days (Warne et al. 2009b). In the above model Δ is a discrimination factor, which is defined as the difference in isotope values between an animal’s tissues and food when feeding on an isotopically pure diet (DeNiro and Epstein 1978). For our mixing model estimates we used discrimination (Δ13C) values resulting from a diet switch study for two species of lizards (Sceloporus undulatus, and Crotaphytus collaris) fed a diet of C4 raised crickets (Warne et al. 2009b). We found the plasma of these lizards had a mean Δ13C = -0.2 ± 0.4‰ VPDB, while crickets fed a C4 based dog food had a Δ13C = -0.9 ± 0.4‰. Reviews of stable isotope ecology have reported Δ13C values for arthropods ranging from -0.5 ± 0.3‰ (Spence and Rosenheim 2005) to 0.3 ± 0.1‰ (McCutchan et al. 2003). Although variation in our assumed Δ13C values would affect proportional estimates of the C3 or C4 resources consumed, the observed trends would not change.

Data analysis:

To compare the seasonal isotope values of consumers between a spring C3 dominated and a summer C4 dominated ecosystem we present the mean δ13C (± SE) of each consumer species during the pre-monsoon (May, June and early-mid-July) and monsoonal periods for each year of this study. We defined the monsoon period to begin with the first day of recorded monsoon rains in July (monsoon 2005 = July 25 to October 15; monsoon 2006 = July 6 to October 15). The effects of seasonal and inter-annual primary production patterns on consumer resource assimilation (δ13C) were determined by two-way ANOVA using the PROC MIXED procedure (Littell et al. 2006) in SAS (SAS 1999). To examine these effects in the lizard community as a whole, lizard species were treated as random effects in the PROC MIXED model. In order to determine the significance of seasonal and year effects post-hoc analyses were conducted using Tukey-Kramer’s hsd test (Sokal and Rohlf 1995). Prior to analysis the data were tested for homogeneity of variance and confirmed to meet the assumptions of ANOVA.

Abstract:

The use of stored resources to fuel reproduction, growth and maintenance to balance variation in nutrient availability is common to many organisms. The degree to which organisms rely upon stored resources in response to varied nutrients, however, is not well quantified. Through stable isotope methods we quantified the use of stored versus incoming nutrients to fuel growth, egg and fat body development in lizards under differing nutrient regimes. We found that the degree of capital breeding is a function of an individual’s body condition. Furthermore, given sufficient income lizards in poor condition can allocate simultaneously to storage, growth, and reproduction, which allowed them to catch up to better conditioned animals. In a parallel, inter-specific survey of wild lizards we found that the degree of capital breeding varied widely across a diverse community. These findings demonstrate that capital breeding in lizards is not simply a one-way flow of endogenous stores to eggs, but is a function of the condition state of individuals and the availability of nutrients during both breeding and non-breeding seasons. Here we explore the implications of these findings for our understanding of capital breeding in lizards and the utility and value of the capital-income concept in general.

Data set ID:

261

Core Areas:

Keywords:

Methods:

Lizard Capture:

For measures of capital breeding in wild lizards, females of seven species were caught April through July of 2008 under the approval of the University of New Mexico institutional animal care and use committee (UNM-IACUC #05MCC004). The species captured were: Cophosaurus texanus, Crotaphytus collaris, Eumeces multivirgatus, Phrynosoma modestum, Sceloporus undulates consubrinus, Urosaurus ornatus, and Uta stansburiana. Lizards deemed by palpation to be egg-bearing were returned to the lab, euthanized and reproductive tissues prepared for stable isotope analysis (see below).

Stable isotope treatments:

After the lizards were euthanized liver, fat body, and thigh muscle samples were harvested, freeze dried and a 0.5 mg sample was placed into a pre-cleaned tin capsule (Costech, #041074, Valencia, CA) for stable isotope analysis. Eggs and follicles were also harvested, their length and width measured and freeze dried. All lipids were extracted from freeze dried and ground muscle and eggs/follicles by a 2:1 chloroform and methanol bath; lizard muscle had undetectable amounts of lipids. The suspended lipids from eggs were pipetted into separate storage vials and air dried. Lipids and lipid-free egg tissues were then loaded into tin capsules. We measured the δ13C of each egg and follicle greater than 6mm in length (½ the length of shelled eggs and assumed to reflect reproductive allocation). Our stable isotope methodology follows standard methods and our protocol is described in detail in Warne et al. (2010a, 2010b). We report all isotope values in the standard delta notation (δX = (Rsample /Rstandard – 1) x 1000) in parts per thousand (‰) relative to the international carbon standard VPDB (Vienna Pee Dee Belemnite). Measurements were conducted on a continuous flow isotope ratio mass spectrometer in the UNM Earth and Planetary Sciences Mass Spectrometry lab. The precision of these analyses was ± 0.1‰ SD for δ13C based on long-term variation of the working laboratory standard (valine δ13C = -26.3‰ VPDB), samples of which were included on each run in order to make corrections to raw values obtained from the mass spectrometer.

Essential to this study is the observation that differences in photosynthetic biochemistry inherent to C3- and C4-plants produces distinct differences in the d13C of their tissues, which can be used to trace the movement of nutrients through consumers (Hobson et al. 1997, O'Brien et al. 2000). Because winter and summer monsoonal rains drive seasonally separated C3 and C4 plant production and resource flux in Chihuahuan Desert food webs (Warne et al. 2010b), we hypothesized that we could use natural variation in the δ13C of C3 and C4 resources to examine capital breeding in wild lizards. We predicted that during the late summer and early fall lizards would develop endogenous lipid stores (capital) from C4 derived sources because C4 plants (primarily grasses) comprise the bulk of primary production during this period. We also hypothesized that reproduction in the spring (the income source) would be fueled by C3 plants associated with winter rains. We subsequently sampled female lizards of a variety of species during April through June 2008 to gauge the relative use of capital (C4) versus income (C3) resources for their first clutch of the season. The lizards were collected from a mixed Creosote and gramma grassland.

We used tissue d13C values and a standard two-end-point mixing model to estimate the proportion of endogenous fat or muscle (capital) and incoming insect-dietary sources used to provision eggs. The mean δ13C value of insects feeding on C3 plants (-27.3‰) served as an income source (see Warne et al. 2010b). The discrimination (Δ13C) values used in this model for muscle (-1.9‰) and fat bodies (0‰) were experimentally determined for S. undulatus (Warne et al. 2010a).

Abstract:

The use of stored resources to fuel reproduction, growth and maintenance to balance variation in nutrient availability is common to many organisms. The degree to which organisms rely upon stored resources in response to varied nutrients, however, is not well quantified. Through stable isotope methods we quantified the use of stored versus incoming nutrients to fuel growth, egg and fat body development in lizards under differing nutrient regimes. We found that the degree of capital breeding is a function of an individual’s body condition. Furthermore, given sufficient income lizards in poor condition can allocate simultaneously to storage, growth, and reproduction, which allowed them to catch up to better conditioned animals. In a parallel, inter-specific survey of wild lizards we found that the degree of capital breeding varied widely across a diverse community. These findings demonstrate that capital breeding in lizards is not simply a one-way flow of endogenous stores to eggs, but is a function of the condition state of individuals and the availability of nutrients during both breeding and non-breeding seasons. Here we explore the implications of these findings for our understanding of capital breeding in lizards and the utility and value of the capital-income concept in general.

Core Areas:

Data set ID:

Keywords:

Methods:

Lizard Capture and Maintenance:

Thirty two female prairie lizards (Sceloporus undulatus) were caught on Bureau of Land Management reserves near Albuquerque, NM during the last two weeks of July, 2007 and maintained in a room at the biology department of the University of New Mexico under the approval of the UNM-IACUC (#07UNM007). Two lizards were housed per 20 gallon glass terrarium and were provided a sand substrate, as well as perch and shelter spaces built by stacked pieces of plywood and rock. Lizards were kept on a 12 hour (light:dark) photoperiod and a temperature gradient was provided by a 100 watt heat lamp placed at one end of the terrarium and focused on the wood perch, which provided a stable heat gradient that ranged from 39 ± 1.7ºC at the perch to 26 ± 0.8ºC at the cool end of the tank. Resulting mean daytime body temperatures were 36.3 ± 6.2ºC (n = 18). An ultraviolet-B fluorescent light (ZooMed® UVB 10.0 fluorescent) was also provided for vitamin D synthesis.

Experimental dietary treatments and reproduction:

S. undulatus were captured from a cottonwood woodland field site and paired by Snout Vent Length (SVL) and then randomly split into either a high (n = 16) or low nutrient treatment (n = 16). The high nutrient diet consisted of seven crickets and two mealworms per week; similar to an ad libitum diet found by Angilletta (2001). We estimated that a low nutrient diet reduced by ~30% of ad libitum (five crickets/week and one mealworm every other week) would reduce body condition and reflect the poor conditions experienced by lizards in the wild (see Ballinger 1977, 1979, Ballinger and Congdon 1980, Sinervo and Adolph 1994). These low diet lizards were switched to the high diet after hibernation, referred to hereafter as the LH treatment (n = 16). The high treatment prior to hibernation was split into a high diet post-hibernation (HH, n = 8) and a low treatment (HL, n = 8). We did not have an LL treatment because we assumed that they would be in such low body condition that they would not reproduce.

The lizards were prepared for hibernation during November 2007 by gradually reducing the photoperiod to 7 hours per day, and were fasted for two weeks. Lizards were then placed in 27 liter plastic containers with a sandy substrate and wood shavings for burrowing on November 17, 2007 and maintained at 10.2 ± 3.1ºC. The lizards were removed from hibernation on February 2, 2008. To induce reproduction, male prairie lizards that were maintained for a separate study were introduced for two weeks to the female terrarium in mid-February of 2008. Reproduction was observed in numerous tanks (mounting and copulation), and signs of reproduction (bite marks) were apparent on all females. The female lizards were then palpated weekly to monitor egg development. When eggs appeared to be nearly shelled or shelled, the lizards were euthanized via an intraperitoneal injection of sodium pentobarbital (using a dose of 60 mg/kg). Two lizards were euthanized in late March following rapid development of shelled eggs. All other lizards were euthanized during the last week of May 2008, at which time most were found to have either large follicles or shelled eggs.

Stable isotope treatments:

After the lizards were euthanized liver, fat body, and thigh muscle samples were harvested, freeze dried and a 0.5 mg sample was placed into a pre-cleaned tin capsule (Costech, #041074, Valencia, CA) for stable isotope analysis. Eggs and follicles were also harvested, their length and width measured and freeze dried. All lipids were extracted from freeze dried and ground muscle and eggs/follicles by a 2:1 chloroform and methanol bath; lizard muscle had undetectable amounts of lipids. The suspended lipids from eggs were pipetted into separate storage vials and air dried. Lipids and lipid-free egg tissues were then loaded into tin capsules. We measured the δ13C of each egg and follicle greater than 6mm in length (½ the length of shelled eggs and assumed to reflect reproductive allocation). Our stable isotope methodology follows standard methods and our protocol is described in detail in Warne et al. (2010a, 2010b). We report all isotope values in the standard delta notation (δX = (Rsample /Rstandard – 1) x 1000) in parts per thousand (‰) relative to the international carbon standard VPDB (Vienna Pee Dee Belemnite). Measurements were conducted on a continuous flow isotope ratio mass spectrometer in the UNM Earth and Planetary Sciences Mass Spectrometry lab. The precision of these analyses was ± 0.1‰ SD for δ13C based on long-term variation of the working laboratory standard (valine δ13C = -26.3‰ VPDB), samples of which were included on each run in order to make corrections to raw values obtained from the mass spectrometer.

Essential to this study is the observation that differences in photosynthetic biochemistry inherent to C3- and C4-plants produces distinct differences in the d13C of their tissues, which can be used to trace the movement of nutrients through consumers (Hobson et al. 1997, O'Brien et al. 2000). The lizards were collected from cottonwood woodlands in which their diet was largely composed of C3-plant derived carbon, as evidenced by a baseline muscle δ13C of -25.1± 0.1‰ VPDB, near that of the mean value for C3 plants of -27.3 ± 0.04‰. Prior to hibernation lizards were maintained on a diet composed of crickets (mean δ13C ± SEM for lipids = -22.5 ± 0.1‰ and lipid free carbon = -21.7 ± 0.1‰ VPDB, n = 16) raised on C3-plant derived dog food (Nutro® Natural Choice® large breed puppy lamb and rice formula) and mealworms (lipids = -26.3 ± 0.1‰ and lipid free = -24.35 ± 0.1‰ VPDB, n = 8) raised on bran meal. Here we used the mathematical normalization model of Post et al. (2007) to determine the lipid-free δ13C values for these insects, assuming reported lipid contents of 13.8% for crickets and 32.8% for mealworms (Bernard and Allen 1997). Maintaining lizards on a C3 diet prior to hibernation insured that their capital stores of fat bodies and muscle would have consistent carbon isotope values. After hibernation the lizards were switched to a C4 based insect diet of crickets (lipids = -16.3 ± 0.1‰ and lipid free = -15.53 ± 0.1‰VPDB, n = 35) raised on a C4 - corn based dog food (Iams® Smart Puppy large breed formulaTM) and mealworms (lipids = -13.0 ± 0.3‰ and lipid free = -10.2 ± 0.2‰ VPDB, n = 9) raised on coarse ground cornmeal; which provided an ‘income’ diet with δ13C values distinct from the pre-hibernation C3 diet.

We used tissue d13C values and a standard two-end-point mixing model to estimate the proportion of endogenous fat or muscle (capital) and incoming insect-dietary sources used to provision eggs. Because crickets and mealworms had different δ13C values and the dietary treatments imposed on the lizards also consisted of differing quantities of feeder insects (high = 7 crickets + 2 mealworms/week; low = 5 + 0.5/week) we used a weighted mean to calculate the insect δ13C for each treatment in this model. The weighted δ13C value for the high dietary treatment for C4 insect lipids was -15.6‰ and -14.3 for lipid free carbon; for the low treatment C4 insect lipids was -16‰ and -15‰ for lipid-free carbon. The discrimination (Δ13C) values used in this model for muscle (-1.9‰) and fat bodies (0‰) were experimentally determined for S. undulatus (Warne et al. 2010a).

Statistical analysis:

The effect of dietary treatment on the body condition of lizards was analyzed by repeated measures ANCOVA with treatment and stage of the experiment as fixed effects, individuals as random effects nested within treatment, and snout-vent length (SVL) as a covariate. Body condition was estimated as the least squares (LS) mean of body weight (minus eggs) adjusted for SVL in this ANCOVA model; a method argued to be more statistically sound than other condition indices (Packard and Boardman 1988, García-Berthou 2001). Treatment effects on SVL were similarly analyzed by repeated measures ANOVA. Mauchly’s test was used to confirm that the assumption of sphericity for repeated measures analysis was valid, and epsilon corrections to the degrees of freedom were applied when necessary. Dietary treatment effects on growth were measured by the specific growth rate of SVL (ln(SVL2/SVL1)/Δdays) for the pre- and post hibernation periods, and analyzed by one-way ANOVA. Dietary treatment effects on reproductive effort, measured as relative clutch mass (RCM = clutch mass/body mass with no eggs) and clutch size were analyzed by one-way ANOVA. The effect of dietary treatment on tissue δ13C values were similarly analyzed by one-way ANOVA. Post-hoc comparisons of treatment effects during the four experimental stages were conducted using Tukey-Kramer’s HSD test. Prior to all analyses the data were tested for homogeneity of variance and confirmed to meet model assumptions. These analyses were performed in JMP® 8.0 (SAS Institute Inc., Cary, NC, 1989-2007). All values are reported as mean ± SEM.

Abstract:

The Sevilleta Gunnison’s Prairie Dog (Cynomys gunnisoni) Restoration project examines keystone consumer (herbivore) effects on grassland in concert with ecological restoration of a “species of greatest conservation need in New Mexico” (NMG&F Comprehensive Wildlife Conservation Strategy, 2007). SevLTER partners directly with Sevilleta National Wildlife Refuge, New Mexico Game and Fish, USFS Rocky Mountain Research Station and non-profit Prairie Dog Pals on this ambitious effort to re-establish Gunnison’s prairie dogs to blue grama dominated (Bouteloua gracilis) Great Plains grassland at the foothills of the Los Pinos Mountains on Sevilleta. While engaged in wildlife management aimed at translocation of approximately 3000 individual prairie dogs, ultimately establishing 5-6 colonies over a 500 ha area, SevLTER is focusing resources on monitoring population dynamics of reintroduced prairie dogs and their effects on vegetation production and diversity, soil disturbance and grasshopper community composition. In this experiment, prairie dogs act as the treatment on a grassland site where the species was extirpated 40 years ago. The long term nature of the project lies in the course of re-establishing prairie dogs combined with the ultimate research goal of describing the functional role of Gunnison’s prairie dogs in an arid grassland ecosystem: first we are challenged to develop and document an economical and efficient management strategy which maximizes reintroduction success and colony survival; second we are tasked with monitoring prairie dog dynamics and their effects on the grassland throughout re-establishment and into a future state, when presumably management intervention will have subsided and we characterize the ecosystem as ‘restored’ – both in the face of highly variable abiotic inputs such as precipitation and temperature and biotic impacts such as predation.

Data set ID:

257

Core Areas:

Keywords:

Related sites:

Prairie Dog Town

Data sources:

sev257_pdog_trapping_20140116

Methods:

Sampling Period

Prairie dogs will be sampled using mark-re-sight methods in the spring (last week of March) and summer (3rd week of June) each year. The justification for this sampling period is to understand overwinter survival and offspring recruitment.

Mark Re-sight Methodology

Prebaiting and Observation Towers

Prior to any trapping, traps in the field are checked to make sure all wooden covers are in place, if not, traps should be repaired as needed.Set 100 traps within each 100m x 100m trapping area.Place traps near active burrows 4 days prior to trapping.At this time trap doors are wired open (make certain all traps are properly wired open) with bait trailing from the outside into the back of (or through) the trap. Traps are baited with sweet feed. Make sure that all traps are functioning properly by testing the trap door sensitivity and adjusting with pliers if needed. Pre-bait traps every morning for 3 sequential days total. All traps should be GPSed and have an adjacent numbered flag and tape with a corresponding number located on the trap.

Trapping

On the morning of the fourth day, well before sunrise, the wires are removed from the traps and the traps then set and baited to capture animals. The traps are all opened well before sunrise, so animals are not disturbed by human activity.This is very important.Prairie dogs are trapped for 3 consecutive mornings.Traps are only left opened during the early morning period, until about 10:00 or 11:00 am, depending on the weather conditions and time of year.Prairie dog activity declines by 10:00-11:00, so even if the weather conditions are fine for continued trapping, trap success after this time will decline dramatically.Traps are collected by around 9:00 am, depending on the weather conditions and time of year, and all trapped animals are brought to a common processing station. At the processing station the trap location, ear tag number, sex, weight, and age of the animal are recorded. It is indicated if the animal is new or a re-capture during this trapping period.If no ear tags are present, new ear tags are clipped to both ears, and the numbers recorded. If one ear tag is missing, another is added to the ear with no tag, and the number recorded. All animals are marked with Nyanzol black dye.For our purposes, it is not necessary to mark each animal with numbers.The goal is to make sure each animal has a clear black mark on its back. Animals at the processing site are kept at all times in the shade and carrots should be given to provide moisture during the heat and stress.Once animals have been processed they are released into their burrow, at the location of their capture. All traps are closed for the day.To make sure all are closed, one person closes all the traps from one of the plots and mark the number on the GPS sheet to note the trap has been closed.

Additional information:

Additional Study Area Information

Study Area Name: Prairie Dog Town

Study Area Location: The study area is about 655 ha (~2.5 sq mi) in size and approximately1 km due west from the foothills of the Los Pinos Mountains. The study is also just north of the Blue Grama Core Site.

Elevation: 1670 m

Soils: sandy loam and sandy clay loam

Site history: historically large prairie dog colonies inhabited the study area

Abstract:

Seasonal environments experience cyclical or unpredictable pulses in plant growth that provide important resources for animal populations, and may affect the diversity and persistence of animal communities that utilize these resources. The timing of breeding cycles and other biological activities must be compatible with the availability of critical resources for animal species to exploit these resource pulses; failure to match animal needs with available energy can cause population declines. Adult Gunnison’s prairie dogs emerge from hibernation and breed in early spring, when plant growth is linked to cool-season precipitation and is primarily represented by the more nutritious and digestible plants that utilize the C3 photosynthetic pathway. In contrast, summer rainfall stimulates growth of less nutritious plants using the C4 photosynthetic pathway. Prairie dogs should therefore produce young during times of increased productivity from C3 plants, while pre-hibernation accumulation of body fat should rely more heavily upon C4 plants. If seasonal availability of high-quality food sources is important to Gunnison’s prairie dog population growth, projected changes in climate that alter the intensity or timing of these resource pulses could result in loss or decline of prairie dog populations. This project will test the hypothesis that population characteristics of Gunnison's prairie dog, an imperiled grassland herbivore, are associated with climate-based influences on pulses of plant growth.

Related sites:

Prairie Dog Town

Blue Grama Grassland (B)

Methods:

Gunnison’s prairie dogs will be monitored at 6 colonies, with 3 colonies each occurring with the range of prairie and montane populations. Colonies for study within the prairie populations occur at Sevilleta National Wildlife Refuge (n = 3 prairie populations) and at Vermejo Park Ranch (n = 3 montane populations). Live-trapping of prairie dogs will be conducted during 3 periods of the active seasons—following emergence (April), after juveniles have risen to the surface (mid-to-late June), and pre-immergence (beginning in August). Trapping will occur for 3-day periods, following pre-baiting with open traps. At capture, sex and body mass of each individual will be recorded. Blood and subcutaneous body fat samples will be collected nondestructively for analysis of isotopic composition. Prairie dogs will be marked with dye, and released on site immediately following processing. After trapping periods at each site have concluded, population counts will be conducted during 2-3 re-sighting (or recapture) periods for each prairie dog colony. Resighting observation periods will be ~3 hours in length, and consist of 2-6 systematic scans of the entire colony, beginning and ending from marked points outside of the colony boundary. During each observation period, prairie dogs will be counted, recorded as marked or unmarked, and location on the colony noted.

Vegetation cover and composition measurements will be collected (or obtained at Sevilleta, where such data is already being collected) during pre- and post-monsoon periods of the active season. Total cover will be measured by plant species (or to genus if species is indeterminable). Total cover will be measured at 12 grid points per colony using Daubenmire frames (0.5 m x 0.5 m), and at 12 grid locations 200-800 m outside of each colony boundary. Adjacent to each Daubenmire frame, a 20 cm x 30 cm sample of vegetation will be clipped and dried for determination of volumetric moisture content of vegetation.

Primary productivity variables (cover, moisture content) will be tested for correlations to individual and population-level condition indicators in prairie dogs. Carbon isotope ratios (δ13C) from prairie dog blood and fat samples will be analyzed on a continuous flow isotope ratio mass spectrometer. The relative contribution of C3 and C4 plants to the diet of each individual will be determined based upon δ13C ratios for C3 and C4 plants in the study area and a 2-endpiont mixing model, and will be calculated for each individual animal, population and season. Population estimates will be calculated using mark-resight estimates, and compared to maximum above-ground counts. The influence of resource pulses on prairie dog population parameters will be tested by comparing the vegetation cover, moisture content, and ratio of total C3:C4 plant cover to the ratio of C3:C4 plants in prairie dog diets, population estimates, and juvenile:adult ratios as an index to population recruitment.

Tissue samples are analyzed for stable carbon isotope ratios in stable isotope laboratory operated by Dr. Zachary Sharp and Dr. Nicu-Viorel Atudorei of the Department of Earth and Planetary Sciences, University of New Mexico.

Keystone species have large impacts on community and ecosystem properties, and create important ecological interactions with other species. Prairie dogs (Cynomys spp.) and banner-tailed kangaroo rats (Dipodomys spectabilis) are considered keystone species of grassland ecosystems, and create a mosaic of unique habitats on the landscape.

Our objective was to evaluate the effects of kangaroo rat mounds on species diversity and composition at a semiarid-arid grassland ecotone. We expected that source populations of plants occurring on kangaroo rat mounds have important influences on species composition of vegetation at the landscape scale, and that these influences differ by grassland type.

Abstract:

Seasonal environments experience cyclical or unpredictable pulses in plant growth that provide important resources for animal populations, and may affect the diversity and persistence of animal communities that utilize these resources. The timing of breeding cycles and other biological activities must be compatible with the availability of critical resources for animal species to exploit these resource pulses; failure to match animal needs with available energy can cause population declines. Adult Gunnison’s prairie dogs emerge from hibernation and breed in early spring, when plant growth is linked to cool-season precipitation and is primarily represented by the more nutritious and digestible plants that utilize the C3 photosynthetic pathway. In contrast, summer rainfall stimulates growth of less nutritious plants using the C4 photosynthetic pathway. Prairie dogs should therefore produce young during times of increased productivity from C3 plants, while pre-hibernation accumulation of body fat should rely more heavily upon C4 plants. If seasonal availability of high-quality food sources is important to Gunnison’s prairie dog population growth, projected changes in climate that alter the intensity or timing of these resource pulses could result in loss or decline of prairie dog populations. This project will test the hypothesis that population characteristics of Gunnison's prairie dog, an imperiled grassland herbivore, are associated with climate-based influences on pulses of plant growth.

Related sites:

Prairie Dog Town

Blue Grama Grassland (B)

Methods:

Gunnison’s prairie dogs will be monitored at 6 colonies, with 3 colonies each occurring with the range of prairie and montane populations. Colonies for study within the prairie populations occur at Sevilleta National Wildlife Refuge (n = 3 prairie populations) and at Vermejo Park Ranch (n = 3 montane populations). Live-trapping of prairie dogs will be conducted during 3 periods of the active seasons—following emergence (April), after juveniles have risen to the surface (mid-to-late June), and pre-immergence (beginning in August). Trapping will occur for 3-day periods, following pre-baiting with open traps. At capture, sex and body mass of each individual will be recorded. Blood and subcutaneous body fat samples will be collected nondestructively for analysis of isotopic composition. Prairie dogs will be marked with dye, and released on site immediately following processing. After trapping periods at each site have concluded, population counts will be conducted during 2-3 re-sighting (or recapture) periods for each prairie dog colony. Resighting observation periods will be ~3 hours in length, and consist of 2-6 systematic scans of the entire colony, beginning and ending from marked points outside of the colony boundary. During each observation period, prairie dogs will be counted, recorded as marked or unmarked, and location on the colony noted. Vegetation cover and composition measurements will be collected (or obtained at Sevilleta, where such data is already being collected) during pre- and post-monsoon periods of the active season. Total cover will be measured by plant species (or to genus if species is indeterminable). Total cover will be measured at 12 grid points per colony using Daubenmire frames (0.5 m x 0.5 m), and at 12 grid locations 200-800 m outside of each colony boundary. Adjacent to each Daubenmire frame, a 20 cm x 30 cm sample of vegetation will be clipped and dried for determination of volumetric moisture content of vegetation. Primary productivity variables (cover, moisture content) will be tested for correlations to individual and population-level condition indicators in prairie dogs. Carbon isotope ratios (δ13C) from prairie dog blood and fat samples will be analyzed on a continuous flow isotope ratio mass spectrometer. The relative contribution of C3 and C4 plants to the diet of each individual will be determined based upon δ13C ratios for C3 and C4 plants in the study area and a 2-endpiont mixing model, and will be calculated for each individual animal, population and season. Population estimates will be calculated using mark-resight estimates, and compared to maximum above-ground counts. The influence of resource pulses on prairie dog population parameters will be tested by comparing the vegetation cover, moisture content, and ratio of total C3:C4 plant cover to the ratio of C3:C4 plants in prairie dog diets, population estimates, and juvenile:adult ratios as an index to population recruitment.